[1] After joining the church, Foster accompanied Joseph Smith, the founder of the Latter Day Saint movement, to Washington, D.C. in March 1840 to help "draft Senate Committee reports"[4] on the Missouri redress issue.
And hearken unto the counsel of my servants Joseph, and Hyrum, and William Law, and unto the authorities which I have called to lay the foundation of Zion;Foster helped build and purchased stock in the resulting Mansion House.
[8] Foster had previously joined discussions in which the murder of Joseph Smith was planned, but never saw these efforts through himself.
After Joseph and Hyrum Smith were shot and killed at Carthage Jail, Foster was "charged and acquitted of their murder.
"[7][9] In a conversation with Abraham Hodge, Foster expressed regret at having played a hand in Joseph's and Hyrum's deaths.